The overall objectives of this study are to clarify further the factors which regulate estrogen and androgen production by mammalian testes. Studies are planned or are in progress to determine the intratesticular site of estrogen formation, the optimal precursor for Beta 17-estradiol formation, and the in vitro and in vivo effects of purified gonadotropins, growth hormone, and prolactin on estrogen and androgen formation and metabolism by intact testes, isolated seminiferous tubules and isolated interstitial tissue. Current studies indicate that the major intratesticular site of estradiol formation is in interstitial tissue. These data were obtained by incubating testicular compartments from human and rat testes with (1,2,6,7(n)-H3 androstenedione.